The proposed plan is for the development of a needle biopsy and needle localization device that can be used with existing mammographic equipment. Using a stereotactic algorithm, this equipment will enable an operator to place a biopsy needle or a localization needle prior to open biopsy of the breast in three dimensions within plus or minus 1-2 millimeters. Since this method utilizes a computer and does not require photographic development, the entire process could be performed in a few minutes. In phase I, components will be selected and procured, software will be developed and an error analysis will be performed. Initial bread-board testing will be performed to verify the feasibility of this method. In phase II, a prototype device will be constructed, clinical testing will be performed, and modifications and improvements will be incorporated into the design.